4. Microbes and humans
Very few microbes are
always pathogenic
Many microbes are
potentially pathogenic
Most microbes are
never pathogenic
5. Host - parasite Interaction
Eukaryotic Cell Pili or adhesins Prokaryotic Cell
Intracellular
Control of virulence factors: Virulent Bacteria
(Pilin, capsule, invasins, toxins etc)
Adherence blockers
Receptor
6. Prokaryotic and Eukaryotic Interactions
Eukaryotic Cell Pili or adhesins Prokaryotic Cell
Intracellular
Control of virulence factors: Virulent Bacteria
(Pilin, capsule, invasins, toxins etc)
Adherence blockers
Receptor
COLONIZATION
7. Prokaryotic and Eukaryotic Interactions
Eukaryotic Cell Pili or adhesins Prokaryotic Cell
Intracellular
Control of virulence factors: Virulent Bacteria
(Pilin, capsule, invasins, toxins etc)
Adherence blockers
Receptor
COLONIZATION INVASION
8. Virulence
The ability of an agent of infection to produce
disease.
The virulence of a microorganism is a measure
of the severity of the disease it causes.
10. Virulence factors help bacteria
• invade the host
• cause disease
• evade host defenses.
Include:
7. Attachment (via adhesins)
8. Colonization
9. Invasiveness
10. Toxins & Enzymes
11. Inhibition of Phagocytosis
11. (Attachment (via adhesins-1
They allow bacteria to
bind to host cells : Cilia - motion
• fimbriae
• some bacterial cell
walls
• capsules
These adhesins bind to
specific epithelium
receptors or they are
able to maintain even
closer contact. Flagellum - motion
12. A
Cell Wall –
Flagellum - protection,
motion invasion, evasion
Cell Parts D
B
Ribosome –
production of Cilia - motion
toxins/attachment
proteins on cell
wall
13. 2-Colonization
• The Ability to Adhere to Host Cells and
Resist Physical Removal or
• the establishment of the pathogen at the
appropriate portal of entry.
• Pathogens usually colonize host tissues
that are in contact with the external
environment.
14. Virulence Factors that Promote Bacterial
Colonization:
3. Using Pili (fimbriae) to Adhere to Host
Cells
4. Using Adhesins to Adhere to Host Cells
5. Using Biofilms to Adhere to Host Cells
15. Invasiveness-3
• the ability of a pathogen to invade tissues.
• Invasiveness encompasses
(1) mechanisms for colonization (adherence and
initial multiplication),
(2) production of extracellular substances
("invasins"), that promote the immediate
invasion of tissues
(3) ability to bypass or overcome host defense
mechanisms which facilitate the actual invasive
process.
17. 4-Toxins &Enzymes
Toxins
• They are products of a
pathogen that destroy/
damage/
• inactivate one or more
vital component of the
host.
• Classes of toxins
Neurotoxins
Enterotoxins
Cytotoxins
18.
19.
20. Enzymes
Excretion of certain
pathogens to assist them
in establishing infection
and producing a disease.
There are virulence
determinant enzymes that
dissolve the glue between
cells, thus allowing the
bacteria to spread rapidly
through the tissue.
22. Inhibition of Phagocytosis
• Ability of Pathogens to Avoid or Overcome
Phagocytes
• Avoiding Contact with Phagocytes
• Inhibition of Phagocytic Engulfment
• Survival Inside of Cells
